Power transmission



Selta. 17, '1940. F. T. HARRINGTN y2,214,817

`POWER TRANSMISSION Filed Jun 27, 195s ATTORNEY Patented Sept. 17, 1940UNITED STATES' Powna 'riuuvsmrssrim Ferris T. Barrington, Detroit,Mich., assignor to Vickers Incorporated, Detroit, Mich., a corporationof Michigan applicati@ Junez'z, 193s, serial No. 215,991

6 Claims.

'I'his invention relates to power transmissions,

, particularly to'those of the type comprising two or more iiuidpressure energy translating devices one of which may function as a pumpand another as a iluid motor. In many transmissions of this characterand particularly with a hydraulic press it is desired to hold themovable platen of the press or other work member under pressure afterright or left by a lever 42. Valve 40 has tank the completion of itspressing stroke. Previously 10 this has beenfaccomplished by allowingthe pump to build up pressure in the press cylinder and using a reliefvalve to prevent this pressure from becoming dangerously high. In thelatter method there is an excessive waste of -power because oi the factthat the -pump delivery is working against the stalled piston of thepress cylinder.

Accumulators have also been used to supply pres-y sureiiuid to the presscylinder, but the pumphad to be bypassed at comparatively highpressures, again wasting power.l v

It is an object of this invention to provide means for holding pressureon a work member by y means other than the delivery of the pump andwithout unnecessary waste o f power. It is 'another Aobject to provide avalve to act vas a relief valve for bypassing the pump when apredetermined safe pressure is exceeded in the hydraulic system, saidvalve also being capable o! bypassing the pump at a pressure lower thanthe aforementioned pressure while the' work member is stalled. Y c

Still another object is to provide an 'accumulator or its equivalent tohold pressure on the press at the end of its pressing stroke togetherwith improved control means for keeping the accumulator filled withoutwasting power.

In the drawing:

tion.

shown in Figure 1.

. Figure 3 is a detail sectional view ola pressurev responsive pilotvalve.

In Figure 1 a pump I8, which may be oi' the4 5 xed displacement type andcontinuously driven b y a prime mover such as an electric motor I2, is

' adapted to draw fluid from a tank I4 vthrough a 'conduit I8. The fluidis delivered through a conduit I8 to a valve 28, which has a spool 22slidably mounted in a. bore 23 and normally held downwardly by@ spring24. 'I'he valve 28 also has a tank port 28 and a delivery port 28.passage y3Il"connects the port 28 to the lower end-of bore 23. Slidablymounted in'passage 38 is a small 5l 32 adapted to raise thespool 22 whenprescheck valve 38 is interposed, to a spring centered,

Figure 1 is a diagrammatic view of the invensure at port 28 rises abovethe setting of the spring 24. A drain passage 33 connects the upper partof the bore 23 to the tank portr28. The port 28 is connected to tank bya conduit 34. The port 28 vis connected by a conduit 38,-in which a 5op'en center four-way valve 48.

The spool of the vlve 48 may be shifted tothe ports 44 and cylinderports 48 and 48. The ports 10 44 are connected to the tank I4 by aconduit 58. The ports '48 and 48 are connected by conduits 52 and 84 tothe head'and rod ends respectively of a large cylinder 58 mounted on apress 58. A piston 88, slidably mounted in the cylinder 15 58, carries aplaten 82 and Iis adapted to press against a base plate 84.

The four-way valve 48 has another port 88 which is always incommunication with pressure line 38 and which isconnected hy a conduit88 to 20 a pressure responsive valve 18 shown in detail in Figure 3.This valve has a spool I2 slidably mounted in a bore 'I4 and held initsleft hand position by a spring 18. A passage 18 connects the .conduit 88to the left end oi' bore l4. This 25 passage is shown as positioned inthevalve body' in Figures l and 2 for sake/"of clearness. .When thepressure in conduit 88 rises above the setting of spring 18, the spool'l2 will shift to the right.V A

conduit 88 extendsgfrom the \valve18 to the'bot-" 30.

tom of the bore `23 invalve 28.- Fluid pressure in conduit 88 is eectiveoverthe full diameter of the valve spool 22 whereas pressure in passage38 is effective only on the smaller area of piston 32. y The valve 'I8has a drain conduit 82 connected to 35 In operation, with the parts inthe'4 position shown in Figure land the pump I Il operating,

iluid is drawn from the tank I4 through conduit I8 and delivered byconduit I8 through valve 20 40 to port 28. Pressure fiuidalso passesthrough passage 38 to piston 32. If.. for any reason pressure shouldbuild up at port 28 and exceed thesetting of -spring 24it will actthrough passage 88 and cause piston 32 to rise which will in turn raise45 the spool 22. Accordingly conduit I8 will be connected to port`28 andbypass the delivery of pump I8 through' conduit 34 to tank.

Normally pressure fluid is delivered from the port 28 of valve 2lithrough conduit 88 and check 50 valve 38 to the four-way valve 48. Thespool of valve 48 being in its center .position there is no fluiddelivered to cylinder 88 and the pump delivery is bypassed to tankthrough the interior of `the spool oi valve 48.

vzo

4vention as shown in Figure 1.

To perform a pressing stroke, the lever 42 is moved to the leftconnecting the delivery conduit 36 to the cylinder port 46 of the valve40. When the lever 42 is moved to the left, fluid is directed throughconduit 52 to the head end of cylinder 56.

Accordingly piston 60 moves downwardly carrying platen 62 to perform thework. Fluid in the rod end of cylinder 56 passes through conduit 54,ports 48 and 44 of valve 40, and conduit 50 to tank.

When the piston 6E reaches the end of its pressing stroke, the lever 42being still held in its left hand position, pressure builds up inconduits 52 and 36 and is transmitted through conduit 68 to the passageI8 of valve 10. When the pressure in passage 18 rises suiiiciently, itsaction in bore 14 on the spool 'l2 causes the latter to shift to theright against the resistance offered by spring 16. Thus conduit 68 isconnected to conduit 80 and fluid is delivered to the bottom of thevbore23 of valve 20. Any fluid that may be trapped on the right side of thespool l2 is drained to tank by the conduit 82. Because of the uiddelivered from port 66 of valve 40 through conduit 68, valve li), andconduit 86 to the bore 23 of valve 20, valve spool 2,2 accordingly risesand bypasses the delivery of the pump. Any fluid that may be trappedabove the spool 22 is drained off through passage 33 to port 26.

High pressure uid is now trapped in the head end of the large cylinder56 and the conduit 52 by check valve 38. The inherent fluid capacitiesand elasticityA of the large cylinder 56 and the conduit 52 produces anaccumulator effect which maintains pressure on the piston 60, therebyholding the platen 62 against the work under pressure. Thus asubstantial interval may elapse before sufficient fluid has leaked outof the pressure side to cause the pressure to drop below the value wherethe spring 16 of valve 'I0 is again able to return spool 12 to the left.When this occurs thepbottom yend of bore 23 is again connected to tankthrough conduits 86 and 82 and spool 22 shifts to its'lower position,thus reloading pump and causing fluid to be delivered to the press cyllinder until the pressure rises sufficiently to again shift valve 10 tothe right. Thus so long as the lever 42 is held to the left, the pumpwill be automatically cut out and cut in as required to maintain thepressure in cylinder 56 within predetermined limits.

To cause theI return stroke of piston 66, the lever 42 of valve 40 ismoved to the right, relieving the pressure in cylinder 56 and conduit 52through ports 46 and 44 of valve 40, to the tank conduit 50. At the sametime pressure uid is delivered from conduit 36, valve 40', port 48 andconduit 54 to the rod end of cylinder 56, causing the return stroke ofthe piston 60.

When the return stroke is completed lever 42 is released and the spoolof valve 40 springcenters, bypassing the pump at low pressure. Anotherpressing stroke may be performed by moving the lever 42 to the left.

Shown in Figure 2 is a modification of the in- The circuit of Figure 2is very similar to that of Figure 1 but is used when the work cylindersuch as 56' is so small as to have insufficient accumulator effect, orwhere for other reasons a separate accumulator is-desirable.

A conduit 52 and a conduit 54 extend from the cylinder ports of closedcenter four-way valve 40 to the head and rod ends respectively ofcylinder 56. Slidably mounted in cylinder 56 is a `all times.

pump is unloaded by the action of valves 10 andl piston 60. A conduit84, which is connected to a spring or gas loaded accumulator 86, passesthrough the discharge port of check valve 38 and is in constantcommunication with the pressure port of the four-way valve 46.

' Because the accumulator is connected between the pump dischargeconduit I8 and the four-way valve 46', the latter may be of the closedcenter type. The valve 'Hl controls the valve 20 in-the same manner aspreviously described, thus maintaining the pressure in conduit 84 andpressure port of valve 40' within predetermined limits at With valve 40in center position the 210 instead of through the four-Way valve 40' asin Figure 1.

If the lever 42 of valve 46 is held to the left after piston 60' hascompleted its working stroke, the action is identical to that of thecircuit in Figure 1. A

The construction disclosed, provides a reliable satisfactory means ofcontrolling the effective op'- eration of a pump in accordance withpressure conditions in a load circuit. The pressure responsive mechanismat the valve l0 may be made extremely small and light and, sincepackings are dispensed with, the spool 12 may be made as nearlyfrictionless in its operation as possible. In addition the travelrequired of. spool 12 between its extreme operating positions beingsmall, the spring 16 may be made many times as long as the spool travel,thus providing a nearly constant force on the spool 12. In fact it isentirely feasible and sometimes desirable to utilize a weight in placeof the spring 16, since the spool 12 may be made extremely smallrelative to theother valves in the circuit and the size or weight thusrequired is not abnormally bulky. The op` eration of4 valve 10 isentirely independent of valve 20 While the valve 26 is entirely andsolely dependent on the valve 10 for its operation during the unloadingand reloading action. These features together contribute to theproduction of an unloader control system which is sufliclently sensitiveto maintain the pressure in the load circuit within predetermined limitswhich are extremely close. In other words, the differential between thepressure at which the pump unloads and that at which it reloads may be avery small percentage of the total pressure in the load circuit.

While rthe form of embodiment of the invention, as'herein disclosed,constitutes a preferred form, it is to be understood that other formsmight be adopted, all coming Within the scope of the claims whichfollow.

What is claimed is as follows:

1. In a Huid power transmission system, pump means forming a source ofpressure fluid, an

accumulator for storing pressure uid, pressure responsive relief valvemeansv to bypass the pump at a predetermined pressure, and additionalpressure responsive valve means connected with the relief valveA tounload the pump at a pressure lower than the rst said pressure.

3. In a uid power transmission system, pump means forming a source ofpressure fluid for use lin a circuit having suiiicien't fluid capacityand elasticity of members under stress to provide an accumulator effect,pressure responsive relief valve means to bypass the pump at apredetermined pressure, and additional pressure responsive meansoperably connected with the relief valve for causing the relief vvalveto unload the pump at a pressure lower than the first said pressure.

4. In a iiuid power transmission system the combination of a iixeddisplacement pump,

means for continuously driving the pump. an accumulator for storingvarying amounts of liquid under pressure, a pilot control meansresponsive to changes in pressure in the accumulator, a valve forbypassing the pump discharge and operating means controlled by the pilotcontrol means for opening said bypass valve when the accumulatorpressure reaches a. predetermined value, said bypass valve being furtherrresponsive to the pump discharge pressure for opening the valvewhenever a predetermined higher pressure is exceeded.

5. In a fluidl power transmission system the combination of a fixeddisplacement pump, means for continuously driving the pump, a'pilotcontrol means responsive to changes in pressure against which the pumpis discharging, a valve for bypassing the pump dischargeI and operatingmeans controlled by the pilot control means for opening said bypassvalve when such.` pressure reaches a predetermined value, said bypassvalve being further responsive to the pump discharge pressure :foropening the valve whenever a prede termined higher pressure is exceeded.

6. In a iiuid power transmission system the combination of a iixeddisplacement pump, means for continuously driving the pump, a pumpdischarge line including a check Valve therein, a pilot control meansresponsive to changes in pressure beyond the check valve, a valve forbypassing the pump discharge and operating means controlled by the pilotcontrol means :for opening said bypass valve when such pressure reachesa predetermined value, said bypass valve being further responsive to thepump discharge pressure for opening the valve whenever a predeterminedhigher pressure is exceeded in the discharge line between the pump andthe check valve.

FERRIS T. HARRINGTON.

